Very many objects made of a thermoplastics material are provided with a decorative design, and it is not possible to enumerate them all here.
These objects are very often manufactured by injecting a suitable thermoplastics material into a mould, the decorative design being applied onto the chosen location of the external surface of the object by any one of well known printing techniques such as silk-screen printing or flexographic printing.
Objects manufactured this way have the drawback that if they are subjected to rubbing during use, the decorative design they carry is easily scratched or even rubbed off.
U.S. Pat. No. 2,811,744 describes a method which avoids this drawback. According to this method, the thermoplastics material is injected directly onto a piece of paper carrying the decorative design printed with a transferable ink, i.e. able to separate from the paper in response to heating, this paper having been previously placed at the desired location in the injection mould.
During the injection, the transferable ink separates from the paper and adheres to the thermoplastics material and, after cooling of the latter, the design is placed on the surface of the object.
However, with this method, there is a substantial risk that the decorative design is deformed or even completely spoiled due to the fact that the molten thermoplastics material moves against the paper during injection.
Moreover, this method is not suitable for manufacturing objects of a thermoplastics material that is flexible at its normal use temperature, because the ink used to form the decorative design diffuses quite easily into such material. The decorative design therefore quite quickly loses its sharpness, which is obviously not desirable.
Also, if this method is used to manufacture objects of a thermoplastics material that is hard at its normal use temperature, the ink forming the decorative design would not diffuse into this material and, even though it is not liable to be deformed by such diffusion, the decorative design would nevertheless be liable to be damaged, or even completely erased, by any rubbing that the object may be subjected to. It is therefore necessary in this instance to protect the decorative design by covering it with a transparent layer of lacquer or plastics material after removal of the object from the injection mould, as is described in the already-mentioned U.S. Pat. No. 2,811,744. The application of this protective layer constitutes an additional operation which complicates the method and makes it more expensive.